1. Field of the Invention
The present invention relates to a film formation apparatus and a film formation method which uses the film formation apparatus.
2. Description of the Related Art
Conventionally, when a thin film is formed on a film formation object such as a substrate by evaporation, sputtering, or the like, in order to control the thickness of the thin film to be formed, a quartz oscillator is placed in a film formation chamber. When a quartz oscillator is placed in the film formation chamber, in forming the thin film, a film forming material forming the thin film is deposited both on the quartz oscillator and on the film formation object. Here, as the film forming material is deposited on the quartz oscillator, the resonance frequency of the quartz oscillator changes according to the amount of the film forming material deposited thereon. Using this phenomenon, the thickness of the film of the film forming material deposited on the film formation object may be known. Specifically, the thickness of the film deposited on the quartz oscillator is calculated from the amount of change in resonance frequency. With the film thickness ratio between the film deposited on the quartz oscillator and the film deposited on the film formation object which is determined in advance, the thickness of the film of the film forming material deposited on the film formation object may be known.
However, as the film forming material is deposited on the quartz oscillator, the relationship between the amount of change in resonance frequency and the thickness value of the film deposited on the film formation object is deviated from the calculated values. Therefore, it is difficult to control the thickness of the film on the film formation object with accuracy for a long period of time.
Japanese Patent Application Laid-Open No. 2008-122200 discloses a method of making smaller a film thickness value error which presents a problem in controlling the thickness of a film on a film formation object. More specifically, in Japanese Patent Application Laid-Open No. 2008-122200, a method is adopted in which, in addition to a conventional quartz oscillator for measurement, a quartz oscillator for calibration for calibrating the deviation of the film thickness value calculated from the amount of change in resonance frequency of the quartz oscillator for measurement is provided in the film formation chamber.
In an ordinary film formation step, first, the film formation object is brought into the film formation chamber, and a film is formed on the film formation object. Here, when the film is formed on the film formation object, the film forming material is deposited on the quartz oscillator for measurement to control the thickness of the film on the film formation object. After the film formation is completed, the film formation object is taken out of the film formation chamber, and the film formation step is completed. However, when the film formation step is repeated multiple times, the film forming material is deposited on the quartz oscillator for measurement each time the film formation step is performed, and thus, the accuracy of the film thickness control is lowered as the film formation step is repeated. Therefore, the quartz oscillator for calibration is used to carry out a calibration step for calibrating the film thickness calculated using the quartz oscillator for measurement.
In the film formation method disclosed in Japanese Patent Application Laid-Open No. 2008-122200, the calibration step is performed between film formation steps, that is, after a film formation step is completed and before the subsequent film formation step is started. In this calibration step, first, the film forming material is deposited both on the quartz oscillator for calibration and on the quartz oscillator for measurement. Then, the thickness of the thin film formed on the film formation object which is determined using the quartz oscillator for calibration (film thickness value P0) and the thickness of the thin film formed on the film formation object which is determined using the quartz oscillator for measurement (film thickness value M0) are measured, and a calibration coefficient P0/M0 is determined. Then, in the film formation step which is performed after the calibration step, by multiplying a film thickness value M1 of the film formation object which is calculated using the quartz oscillator for measurement by the calibration coefficient P0/M0 which is determined in advance, the thickness of the film on the film formation object is controlled with accuracy.
On the other hand, Japanese Patent Application Laid-Open No. 2004-091919 discloses an apparatus and a method for forming a film having a uniform thickness on a surface of a film formation object. In the thin film formation apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-091919, a movable film formation source moves with constant speed below a fixed film formation object. By forming a thin film using the thin film formation apparatus, a film having a uniform thickness may be formed on the film formation object even if the film formation object has a large area.
Further, in the thin film formation apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-091919, in order to monitor the amount of the film forming material released from the film formation source, a film thickness sensor (corresponding to quartz oscillator for measurement) is provided which is fixed above a waiting position of the film formation source. The film thickness sensor may detect the film forming speed of the film forming material, and thus, at the time when the film forming speed reaches a desired level, the film formation source moves to a film forming position to form a film on the film formation object.
As described above, in Japanese Patent Application Laid-Open No. 2008-122200, the calibration step is performed between film formation steps. However, when the calibration step is performed between film formation steps, the film is not formed on the film formation object during that period, and thus, there is a problem that the productivity is lowered.
On the other hand, in Japanese Patent Application Laid-Open No. 2004-091919, the film thickness sensor is fixed at the waiting position of the film formation source (the position at which the film is not formed on the film formation object), and thus, the film thickness sensor cannot monitor the amount of the film forming material released from the film formation source during the film formation step. Therefore, even if the quartz oscillator for calibration disclosed in Japanese Patent Application Laid-Open No. 2008-122200 is provided in the thin film formation apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-091919, it is impossible to carry out the calibration step during the film formation step.